The disclosed subject matter relates generally to managing the power usage of a device that uses stored energy to attempt to increase the length of time the device can be operated without depleting the source of stored energy.
Many electrical devices are provided with electrical energy from renewable energy sources, such as solar or wind. A power generator, such as a solar panel or wind turbine, provides electrical energy for the device. To compensate for time periods when power is not being generated (e.g., during periods of darkness or when there is no wind), an energy storage device, such as a battery, is typically employed to power the device. The amount of time that the device can be powered by the battery depends on factors such as the capacity of the battery, the power demanded by the load, and the amount of energy that is stored in the battery when the power generator is active (i.e., during daylight hours or in the presence of wind). Typically, designers select the battery capacity based on the expected service conditions of the device. However, during abnormal environmental conditions, such as prolonged bad weather, it is possible that the battery may not be charged sufficiently during the charging portion of the day to maintain its level of charge. Eventually, the battery may be depleted and the device may cease to operate. Increasing the battery capacity to broaden the range of environmental conditions under which the system may maintain an adequate charge increases the weight and cost of the battery.
There have been various attempts to optimize the use of solar energy stored in rechargeable batteries to provide longer run times for loads such as light emitting diodes (LEDs) that are powered from these batteries. For example, one technique monitors and stores the battery voltage at the start of a selected time interval and adjusts the brightness of the LEDs by evaluating the battery voltage. One difficulty with this method is that the actual amount of energy stored in the rechargeable battery is not a linear function of battery voltage. In some applications, when fully charged, the battery voltage might decrease only 10% as more than 70% of the battery power is consumed. Then, as the battery is becoming more discharged, the battery voltage might decrease by 30% as 20% of the battery power is consumed. Therefore, using the battery voltage as an indicator of remaining battery power capacity suffers from such non-linear characteristics.
This section of this document is intended to introduce various aspects of art that may be related to various aspects of the disclosed subject matter described and/or claimed below. This section provides background information to facilitate a better understanding of the various aspects of the disclosed subject matter. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art. The disclosed subject matter is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.